Quoting Massimo Sgaravatto (massimo.sgaravatto@xxxxxxxxx): > Thank you > > But the algorithms used during backfilling and during rebalancing (to > decide where data have to be placed) are different ? Yes, the balancer takes more factors into consideration. It also takes into consideration all of the pools and can make smarter decisions. We noticed way less data movement when using balancer than expected. > I.e. assuming that no new data are written and no data are deleted, if you > rely on the standard way (i.e. backfilling), when the data movement process > finishes (and therefore the status is HEALTH_OK), can the automatic > balancer (in upmap mode) decide that some data have to be re-moved ? Yes, for sure. Cephs balancing is not perfect (because # PGs is less than you need for ideal placement). You can look at "ceph osd df" and look at the standard deviation. If that is quite high it makes sense to use balancer to equalize to otain higher utilization. Either PG optimized or capactity optimized (or a mix of both, default balancer settings). Gr. Stefan -- | BIT BV https://www.bit.nl/ Kamer van Koophandel 09090351 | GPG: 0xD14839C6 +31 318 648 688 / info@xxxxxx _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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